Loading table and heat treating apparatus having the loading table

ABSTRACT

A thermal processing system has a processing vessel  4 , a support post  30  stood on the bottom wall of the processing vessel  4 , and a support table  32  internally provided with a heating means  38  and supported on the support post  30 . A workpiece W is placed on the upper surface of the support table  32  and is subjected to a predetermined thermal process. The upper, the side and the lower surface of the support table  32  are covered with heat-resistant covering members  72, 74  and  76  to prevent the thermal diffusion of metal atoms causative of contamination from the support table  32 . thus, various types of contamination, such as metal and organic contamination, can be prevented.

TECHNICAL FIELD

The present invention relates to a support table structure forsupporting a workpiece, such as a semiconductor wafer, and a thermalprocessing system provided with the same.

BACKGROUND ART

A workpiece, such as a semiconductor wafer, is subject repeatedly tosingle-wafer processing processes, such as a film deposition process, anetching process, a thermal process, a modifying process and acrystallization process to build a desired semiconductor integratedcircuit on the workpiece. Those processes use necessary process gases.For example, the film deposition process uses film forming gases, themodifying process uses ozone gas, the crystallization process uses aninert gas, such as N₂ gas, and O₂ gas. Those process gases are suppliedinto a processing vessel.

For example, a single-wafer thermal processing system for processing asingle wafer at a time by a heat treatment process places a supporttable internally provided with, for example, a resistance heater in aprocessing vessel capable of being evacuated, supplies predeterminedprocess gases into the processing vessel after mounting a semiconductorwafer on top of the support table, and processes the wafer by variousthermal processes under predetermined process conditions.

The support table is disposed in the processing vessel with its surfaceexposed to the atmosphere in the processing vessel. Therefore, a smallamount of heavy metals contained in materials of which the support tableis made, for example, a ceramic material, such as AlN, and metallicmaterials is caused to diffuse into the interior space of the processingvessel by heat. Those diffused substances cause metal contamination andorganic contamination. Very severe contamination preventing measureshave been desired to prevent metal contamination and organiccontamination in recent years where organometallic compounds are used assource gases for film deposition.

Usually, the heater incorporated into the support table is divided intoa plurality of concentric circular sections. The respective temperaturesof the sections are controlled individually to heat the support table inan optimum temperature distribution for processing a wafer. Ifmagnitudes of power supplied to the sections of the heater are greatlydifferent from each other, parts of the support table respectivelycorresponding to the sections of the heater are subject to greatlydifferent thermal expansions, respectively, and, in some cases, thesupport table breaks. The insulation resistance of AlN decreases greatlyand leakage current flows when AlN is exposed to high-temperature heat.Therefore, process temperature has been unable to be increased beyondabout 650° C.

When the thermal process is a film deposition process for depositing athin film on a surface of a wafer, unnecessary films are depositedinevitably on the surface of the support table and the inside surfacesof the processing vessel in addition to the deposition of a desired filmon a surface of the wafer. If the unnecessary films come of the surfacesof the support table and the processing vessel, particles that reduceproduct yield are produced. A cleaning process is executed periodicallyor at indeterminate intervals to remove the unnecessary films. Thecleaning process etches off the unnecessary films by supplying anetching gas into the processing vessel or removes the unnecessary filmsby immersing structural members disposed inside the processing vessel inan etchant, such as a nitric acid solution.

A technique for contamination prevention or reducing the frequency ofthe cleaning process proposed in JP 63-278322 A forms a support table bycovering a heating element with a quartz casing. A technique for thesame purpose proposed in JP 07-078766 A uses a support table constructedby placing a resistance heating element in a quartz case. Techniquesproposed for the same purpose in JP 03-220718 A and JP 06-260430 A use asupport table formed by sandwiching a heater between quarts plates.

Those prior art techniques using a support table covered with a quartzcover are effective in suppressing contamination, such as metalcontamination, to some extent. However the effect of the prior arttechniques is not fully satisfactory. When the quarts plates aretransparent, a temperature distribution on the heating element isreflected on the temperature of the wafer and the wafer is hated in anuneven intrasurface temperature distribution. Moreover, in some cases,unnecessary films are deposited in patches or irregularities on the backsurface of the support table or on a cover covering the back surface ofthe support table. Since thick parts and thin parts of the unnecessaryfilms deposited in patches or irregularities have differentemissivities, respectively. Consequently, temperature is distributed inan uneven temperature distribution on the surface of the support table,intrasurface temperature distribution on the water becomes uneven, andthermal process to the wafer cannot be achieved uniformly.

The unnecessary films deposited on the surfaces of the support table andthe cover peel of comparatively easily at an early stage. Since thecleaning process needs to be carried out before the unnecessary filmspeel off, maintenance work including the cleaning process needs to becarried out frequently at short intervals. When the support table,namely, a heating structure, is divided into heating zones which can beindividually heated and the levels of power supplied to the zones aredistributed in a wide range, the support table may possibly break due tothe different thermal expansions of the materials forming the zones ofthe support table.

The present invention has been made in view of those problems to solvethose problems effectively.

Accordingly, it is an object of the present invention to provide asupport table structure capable of surely suppressing the occurrence ofcontamination, such as metal contamination, having high heatconductivity, suitable for a high-temperature thermal process andcapable of being heated uniformly by wide-range adjustment, and toprovide a thermal processing system provided with the support tablestructure.

Another object of the present invention is to provide a support tablestructure capable of eliminating the detrimental thermal effect ofunnecessary films deposited in patches thereon and of maintaining thesurface thereof in a highly uniform intrasurface temperaturedistribution, and to provide a thermal processing system provided withthe support table structure.

A third object of the present invention is to provide a support tablestructure capable of effectively preventing unnecessary films depositedthereon to reduce the frequency of maintenance work, such as a cleaningprocess, and to provide a thermal processing system provided with thesupport table structure.

A fourth object of the present invention is to provide a support tablestructure including a support table having a plurality of hating zonesand capable of maintaining the surface of the wafer in a highly uniformintrasurface temperature distribution by setting differences in drivingpower flexibility among the heating zones and of performing a specialheating process, and to provide a thermal processing system providedwith the support table structure.

DISCLOSURE OF THE INVENTION

The present invention provides a support table structure in a firstaspect of the present invention including: a support table, forsupporting a workpiece thereon to subject the workpiece to apredetermined thermal process in a processing vessel, provided with aheating means for heating the workpiece; and a support post standing onthe bottom of the processing vessel and supporting the support table;characterized by a heat-resistant upper surface covering member, aheat-resistant side surface covering member and a heat-resistant lowersurface covering member respectively covering the upper, the side andthe lower surface of the support table.

Since the upper, the side and the lower surface of the support table forsupporting the workpiece thereon are covered with the heat-resistantcovering members, thermal diffusion of contaminative metal atoms fromthe support table can be prevented, and contamination, such as metalcontamination and organic contamination, can be prevented.

The present invention provides a support table structure in a secondaspect of the present invention including: a support table, forsupporting a workpiece thereon to subject the workpiece to apredetermined thermal process in a processing vessel, provided with aheating means for heating the workpiece; and a support post standing onthe bottom of the processing vessel and supporting the support table;characterized by a heat-resistant, opaque back cover disposed under thelower surface of the support table.

Since the heat-resistant, opaque back cover is disposed under the lowersurface of the support table, the distribution of emissivity on thesurface of the opaque back cover remain substantially uniform even ifunnecessary films are deposited in patches (irregularities) on thesurface (lower surface). Consequently, the support table and theworkpiece can be heated in a high intrasurface temperature distribution.

In the support table structure in the second aspect of the presentinvention, the upper and the side surface of the support table and thelower surface of the opaque back cover may be covered with upper, sideand lower surface covering members, respectively.

When the upper and the side surface of the support table and the lowersurface of the opaque back cover member are thus covered with the upper,the side and the lower surface covering member, respectively, thermaldiffusion of contaminative metal atoms from the support table can beprevented, and contamination, such as metal contamination and organiccontamination, can be prevented.

In the support table structure in first or the second aspect of thepresent invention, the upper cover member may have a diametersubstantially equal to that of the support table, a raised part may beformed on the upper surface of the upper surface covering member, and arecess for receiving the workpiece may be formed in the raised part.

In the support table structure in the first or the second aspect of thepresent invention, the upper surface of a peripheral part of the uppersurface covering member may be contiguously covered with a part of theside surface covering member.

In the support table structure in the first or the second aspect of thepresent invention, the side surface of the support table may be coveredwith an opaque covering member made of opaque quartz glass.

In the support table in the second aspect of the present invention, aspace may be formed between the opaque back cover and the lower surfacecovering member.

In the support table in the second aspect of the present invention,projections may project from the lower surface of the opaque back coverto define the space between the opaque back cover and the lower surfacecovering member.

The present invention provides a support table structure in a thirdaspect of the present invention including: a support table forsupporting a workpiece thereon to subject the workpiece to apredetermined thermal process in a processing vessel; and a support poststanding on the bottom of the processing vessel and supporting thesupport table; characterized in that the support table and the supportpost are made of quartz glass, and a heating means is embedded in thesupport table.

Since the support table is made of quartz glass, thermal diffusion ofcontaminative metal atoms from the support table can be prevented, andcontamination, such as metal contamination, can be prevented.

In the support table structure in the third aspect of the presentinvention, the support post may have a cylindrical shape, and powersupply lines for supplying power to the heating means may be passedthrough a central part of the support table and may be extended throughthe cylindrical support post.

In the support table structure in the third aspect of the presentinvention, the support table may be built by bonding together a topplate, a middle plate and a bottom plate, wiring grooves for holding theheating means may be formed in either the lower surface of the top plateor the upper surface of the middle plate, and a wiring groove forholding the power supply lines connected to the heating means may beformed in either the lower surface of the middle plate or the uppersurface of the bottom plate.

In the support table structure in the third aspect of the presentinvention, the upper surface of the support table may be covered with anopaque temperature-equalizing plate.

The opaque temperature-equalizing plate improves the uniformity ofintrasurface temperature distribution on the workpiece.

In the support table structure in the third aspect of the presentinvention, the support table may be provided with a purging gas supplypore to supply a purging gas over the upper surface of the supporttable, and a gas supply quartz pipe may be connected to the purging gassupply pore.

In the support table structure in the third aspect of the presentinvention, the quartz pipe may be extended outside the support post andmay have upper and lower ends welded to the support table and thesupport post, respectively.

In the support table structure in the third aspect of the presentinvention, the quartz glass may be transparent.

In the support table structure in the third aspect of the presentinvention, a heat-resistant, opaque back cover may be disposed under thelower surface of the support table.

When the heat-resistant, opaque back cover is disposed under the lowersurface of the support table, the emissivity of the surface of theopaque back cover remain substantially uniform even if unnecessary filmsare deposited in patches (irregularities) on the surface (lower surface)of the opaque back cover. Consequently, the surface of the support tableand the workpiece can be heated in highly uniform intrasurfacetemperature distribution.

In the support table structure in the third aspect of the presentinvention, the upper, the side and the lower surface of the supporttable may be covered with upper, side and lower surface coveringmembers, respectively.

When the upper, the side and the lower surface of the support table arecovered with the upper, the side and the lower surface covering member,respectively, thermal diffusion of contaminative metal atoms and suchfrom the support table can be prevented and hence various types ofcontamination, such as metal contamination, can be prevented.

When the support table and the side and the lower surface coveringmember are made of quartz, contamination, such as metal contaminationdue to the thermal diffusion of contaminants from the support table andthe side and the lower surface covering member can be suppressed andsupport table can be prevented from being exposed to source gases.Consequently, interval between the successive wet cleaning cycles forcleaning the support table can be extended, the life of the supporttable can be extended, and the support table can be kept in its initialshape for a long time.

In the support table structure in the third aspect of the presentinvention, the support post is stood up on a cushioning member toprevent the breakage of the support post.

In the support table structure in the second or the third aspect of thepresent invention, the opaque back cover is made of opaque quartz glass.

In the support table structure in the first, the second or the thirdaspect of the present invention, the side surface of the support postmay be covered with a heat-resistant support post covering member.

When the support post supporting the support table is thus covered withthe support post covering member, metal contamination can be preventedand the support post can be prevented from being exposed to sourcegases.

In the support table structure in the first, the second or the thirdaspect of the present invention, the upper, the side and the lowersurface covering member and the support post covering member mayconstitute a cover assembly, the lower surface covering member and thesupport post covering member may be formed integrally in a singlemember, and the cover assembly may be able to be assembled anddisassembled.

The cover assembly that can be assembled and disassembled facilitatesquickly completing maintenance work, such as cleaning by a wet cleaningprocess.

In the support table in the second or the third aspect of the presentinvention, the covering members excluding the upper surface coveringmember and the opaque back cover may be made of transparent quartzglass, and the surfaces of the covering members made of transparentquartz glass may be finished by a surface roughening process to preventfilms deposited thereon from peeling off.

Unnecessary films deposited on the surfaces of the covering members andlikely to peel off and to produce particles cannot easily peel off.Therefore, the period of maintenance work, namely, the cleaning process,can be extended.

In the support table in the first, the second or the third aspect of thepresent invention, a sealing member may be disposed near a lower joiningpart of the support post, and the sealing member may be shielded fromheat radiated by the support table by an opaque shielding member.

The sealing member disposed near the lower joining part of the supportpost can be shielded from heat radiated by the support table by theopaque shielding member to protect the sealing member from damaging byheat.

In the support table in the first, the second or the third aspect of thepresent invention, the support post may be made of an opaque material,the support post may be internally provided with an opaque member toprotect the sealing member disposed near the lower joining part of thesupport post from heat radiated by the support table.

The present invention provides a thermal processing system in a fourthaspect of the present invention including: a processing vessel capableof being evacuated; the support table structure in the first, the secondor the third aspect of the present invention; and a gas supply systemfor supplying process gases into the processing vessel.

In the thermal processing system in the fourth aspect of the presentinvention, the heating means for heating the support table is dividedinto inner and outer heating sections respectively corresponding toinner and outer zones in the support table.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a thermal processing systemembodying the present invention provided with a support table structureembodying the present invention;

FIG. 2 is a sectional view of a support table structure in a firstembodiment according to the present invention;

FIG. 3 is an exploded perspective view of a cover structure included inthe support table structure shown in FIG. 2;

FIG. 4 is a sectional view of a support table structure in a secondembodiment according to the present invention;

FIG. 5 is an enlarged, fragmentary sectional view of a lower end part ofa support post included in the support table structure shown in FIG. 4;

FIG. 6 is an enlarged sectional view of a part of a support tableincluded in the support table structure shown in FIG. 4;

FIG. 7 is an exploded sectional view of the support table included inthe support table structure shown in FIG. 4;

FIG. 8 is an exploded perspective view of a cover structure included inthe support table structure shown in FIG. 4;

FIG. 9 is a graph showing the dependence of intrasurface temperaturedistribution on a support table on pressure;

FIG. 10 is a sectional view of a support table structure in amodification of the support table structure in the second embodiment;

FIG. 11 is a sectional view of a support table structure in anothermodification of the support table structure in the second embodiment;

FIG. 12 is an exploded perspective view of the support table structureshown in FIG. 11; and

FIG. 13 is a sectional view of a support table structure in a thirdembodiment according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A thermal processing system embodying the present invention andincluding a support table structure embodying the present invention willbe described with reference to FIGS. 1 to 13.

FIGS. 1 to 3 show a thermal processing system provided with a supporttable structure in a first embodiment according to the presentinvention.

FIG. 1 is a schematic sectional view of a thermal processing systemembodying the present invention provided with a support table structureembodying the present invention, FIG. 2 is a sectional view of a supporttable structure in a first embodiment according to the present inventionand FIG. 3 is an exploded perspective view of a cover structure includedin the support table structure shown in FIG. 2.

Referring to FIGS. 1 to 3, a thermal processing system 2 has aprocessing vessel 4 made of aluminum and defining, for example, asubstantially cylindrical processing space S. The processing vessel 4has a top wall provided with a shower head 6. Process gases, such assource gases, are supplied through the shower head 6 into the processingvessel 4. Gases are jetted through gas jetting holes formed in a gasjetting wall 8 included in the shower head 6 into the processing space Sof the processing vessel 4.

The interior of the shower head 6 is divided into tow gas diffusionchambers 12A and 12B. The gas supplied into the shower head 6 isdiffused horizontally and then is jetted through gas jetting holes 10Aand 10B communicating with the gas diffusion chambers 12A and 12B intothe processing space S. The gas jetting holes 10A and 10B are arrangedin an array. The shower head 6 is made of, for example, nickel, a nickelalloy, such as Hastelloy®, aluminum or an aluminum alloy. The showerhead 6 may have a single diffusion chamber. A sealing member 14, such asan O ring, is held at the joint of the shower head 6 and the open upperend of the processing vessel 4 to seal the processing vessel 4hermetically.

The processing vessel 4 has a side wall provided with an opening 16. Asemiconductor wafer W is carried into and carried out of the processingvessel 4 through the opening 16. The opening 16 is closed hermeticallyby a gate valve 18.

The processing vessel 4 has a bottom wall 20 surrounding an exhausttrapping space 22. More specifically, the bottom wall 20 is providedwith a large central opening 24. A bottomed cylindrical member 26 isfitted in the central opening 24 of the bottom wall 20 so as to extenddownward from the bottom wall 20. The bottomed cylindrical member 26defines the exhaust trapping space 22. The bottomed cylindrical member26 has a bottom wall 28. A support table structure 29 embodying thepresent invention is stood up on the bottom wall 28. The support tablestructure 29 has a cylindrical support post 30 made of a ceramicmaterial, such as AlN, and a support table 32 connected to the upper endof the support post 30.

An entrance 24 of the exhaust trapping space 22 has a diameter smallerthan that of the support table 32. The process gas flows down through aspace around the circumference of the support table 32 into a spaceextending under the support table 32 and then flows down through theentrance 24 into the exhaust trapping space 22. An exhaust opening 34 isformed in a lower part of the side wall of the cylindrical member 26 soas to open into the exhaust trapping space 22. An exhaust pipe 36 hasone end connected to the exhaust opening 34 and the other end connectedto a vacuum pump, not shown. The vacuum pump evacuates the processingspace S in the processing vessel 4 and the exhaust trapping space 22.

A pressure regulating valve, not shown, provided with an adjustablevalve element is placed in the exhaust pipe 36. The pressure regulatingvalve is able to regulate its opening automatically to maintain theinterior of the processing vessel at a desired pressure or to adjust thepressure quickly to a desired pressure.

The support table 32 is provided internally with a resistance heater 38made of, for example, molybdenum in a predetermined pattern. Theresistance heater 38 is embedded in a sintered ceramic layer made of,for example, AlN. The support table 32 is capable of supporting asemiconductor wafer W on its upper surface. Power supply conductors 40extended through the support post 30 are connected to the resistanceheater 38 to supply controlled power to the resistance heater 38. Thepower supply conductors 40 are extended in quartz pipes 39,respectively, and are connected to a power supply cable in a lower partof the support post 30. The resistance heater 38 is divided intoconcentric inner and outer heating sections. Magnitudes of powersupplied to the inner and the outer section are controlled individually.Although only the two power supply conductors 40 are shown in FIG. 2,actually, four power supply conductors 40 are connected to theresistance heater 38.

The support table 32 is provided with, for example, three verticalthrough holes 41. Only two of the three vertical through holes 41 areshown in FIG. 1. Lifting pins 42 are loosely fitted in the verticalthrough holes 41 so as to be able to move vertically. The lifting pins42 rest on a circular raising ring 44 made of a ceramic material, suchas alumina, and disposed below the lifting pins 42. An arm 45 extendingfrom the raising ring 44 is connected to a vertically movable raisingrod 46 penetrating the bottom wall 20 of the processing vessel 4. Theraising rod 46 can be vertically moved by an actuator 48. The liftingpins 42 are elevated so as to project upward from the vertical throughholes 41 to receive or to send out a wafer W. A part, penetrated by theraising rod 46, of the bottom wall 20 is covered with a stretchablebellows 50 to keep the processing vessel 4 hermetically sealed duringthe vertical movement of the raising rod 46.

Referring to FIG. 2, the cylindrical support post 30 fixedly supportingthe support table 32 is made of, for example, AlN. A flange 52 is formedon the lower end of the support post 30. In FIG. 2, the interiorstructural members and the lifting pins 42 are omitted. The bottom wall28 is provided with a central opening 54 of a predetermined size. A baseplate 56 made of, for example, an aluminum alloy and having a diameterslightly greater than that of the base plate 56 is placed on the uppersurface of the bottom wall 28 and is fastened to the bottom wall 28 withbolts 58. A sealing member 60, such as an O ring, is held between theupper surface of the bottom wall 28 and the lower surface of the baseplate 56 to seal hermetically the gap between the bottom wall 28 and thebase plate 56. The support post 30 is stood on the base plate 56. Aholding member 62 is made of, for example, an aluminum alloy and has theshape of a ring having an inverted L-shaped cross section. The holdingmember 62 is put on the flange 52 so as to cover the flange 52 and theholding member 62 is fastened to the base plate 56 with bolts 64 to holdthe flange 52 fixedly between the holding member 62 and the base plate56. A sealing member 66, such as an O ring, is held between the uppersurface of the base plate 56 and the lower surface of the flange 52 toseal hermetically the gap between the base plate 56 and the flange 52.The base plate 56 is provided with a plurality of through holes 68. Thepower supply conductors 40 are extended outside through the throughholes 68. The interior of the cylindrical support post 30 is at theatmospheric pressure. The upper end of the support post 30 is fixedlyand hermetically joined to a central part of the back surface of thesupport table 32 by welding or the like. The support post 30 may beairtightly sealed.

A cover assembly featuring the present invention is combined with thesupport table structure 29. Referring to FIG. 3, the cover assembly isformed by assembling an upper surface covering member 72 having theshape of a disk and capable of covering a wafer support part, forsupporting a semiconductor wafer W thereon, of the upper surface of thesupport table 32, a peripheral surface covering member 74 having theshape of a ring and capable of covering a peripheral part of the supporttable 32 and of partly or entirely covering the side surface of thesupport table 32, a lower surface covering member 76 capable of partlyor entirely covering the side surface of the support table 32 and ofcovering the lower surface of the support table 32, a support postcovering member 78 capable of entirely covering the side surface of thesupport post 30, and a lower end covering member 80 for covering a lowerend part of the support post 30. An opaque back cover 82 having anannular shape is held in contact with the lower surface (back surface)of the support table 32 between the lower surface of the support table32 and the lower surface covering member 76. The lower surface coveringmember 76 covers the lower surface of the opaque back cover 82.

Those covering members 72, 74, 76, 78 and 80 and the back cover 82 aremade of heat-resistant, corrosion-resistant materials. Since a wafer Wis seated directly on the upper surface covering member 72, the uppersurface covering member is made of a ceramic material scarcely causingcontamination, such as metal contamination or organic contamination, andhaving a high thermal conductivity, such as SiC. The opaque back cover82 is made of a material scarcely causing contamination, such as metalcontamination or organic contamination, and scarcely transmitting heat,such as opaque quartz glass. The other covering members 74, 76, 78 and80 are made of a material scarcely causing metal contamination ororganic contamination, such as transparent quartz glass.

The upper surface covering member 72 made of SiC having a high thermalconductivity has the shape of a circular plate. The upper surfacecovering member 72 is provided with a central recess 84 for receivingand supporting a wafer W directly therein. The depth of the centralrecess 84 is approximately equal to the thickness of the wafer W. Theupper surface covering member 72 is provided with through holes 41through which the lifting pins 42 (FIG. 1) extend upward. The thicknessof the upper surface covering member 72 is, for example, on the order of3.0 mm.

The peripheral surface covering member 74 made of transparent quartzglass has the shape of a ring having an inverted L-shaped cross section.The peripheral surface covering member 74 covers a peripheral part ofthe upper surface of the support table 32 and partly or entirely coversthe side surface of the support table 32. The peripheral surfacecovering member 74 can be removably seated on a peripheral part of thesupport table 32 as shown in FIG. 2. An annular step 86 is formed in theinside surface of the peripheral surface covering member 74. The uppersurface covering member 72 is detachably supported on the peripheralsurface covering member 74 with a peripheral part thereof seated on theannular step 86. The thickness of the peripheral surface covering member74 is, for example, between about 2.0 and about 3.0 mm.

The lower surface covering member 76 made of transparent quartz glassand the support post covering member 78 made of transparent quartz glassare joined together by welding. The lower surface covering member 76 isa circular vessel capable of partly or entirely covering the sidesurface of the support table 32 and of entirely covering the lowersurface of the support table 32. The lower surface covering member 76 isprovided in its central part with an opening 88 for receiving an upperend part of the support post 30 as shown in FIG. 2. The upper end of thesupport post covering member 78 is welded to the edge of the opening 88.The lower surface covering member 76 is capable of removably receivingthe entire support table 32 therein. The inside diameter of the sidewall of the peripheral surface covering member 74 is slightly greaterthan the outside diameter of the side wall of the lower surface coveringmember 76. As shown in FIG. 2, the peripheral surface covering member 74and the lower surface covering member 76 are separably combined togethersuch that the side wall of the lower surface covering member 76 isfitted closely in the side wall of the peripheral surface coveringmember 74 and the respective lower end surfaces of the peripheralsurface covering member 74 and the lower surface covering member 76 areflush with each other.

Thus, the side surface of the support table 32 is completely covered.Through holes 41 are formed in the bottom wall of the lower surfacecovering member 76. The lifting pins 42 (FIG. 1) are extended throughthe through holes 41.

The support post covering member 78 welded to the lower surface coveringmember 76 has an inside diameter slightly greater than the outsidediameter of the flange 52. The support post covering member 78 is seatedon the holding member 62 as shown in FIG. 2. When the support table 32needs to be removed, the assembly of the lower surface covering member76 and the support post covering member 78 is pulled down relative tothe support post 30 to separate the lower surface covering member 76from the support table 32. The lower surface covering member 76 has awall thickness, for example, on the order of 3.0 mm and the support postcovering member 78 has a wall thickness, for example, on the order of5.0 mm.

The lower end covering member 80 made of transparent quartz glass isformed in the shape of a ring having an inverted L-shaped cross sectionto cover the exposed surfaces of the holding member 62 and the baseplate 56. The lower end covering member 80 is a half ring split into twohalves to facilitate putting the lower end covering member 80 in placeand removing the same. The lower end covering member 80 does notnecessarily need to be split and may be formed in a single piece.

The flange 52 has a diameter slightly smaller than the inside diameterof the support post covering member 78. The support post 30 can bepulled upward and can be extracted from the support post covering member78 after unfastening the bolts 58 and 64 and removing the base plate 56and the holding member 62.

The opaque back cover 82 is formed in an annular shape to cover theentire lower surface (back surface) of the support table 32 excluding apart joined to the support post 30. The support post 30 is passedthrough a central opening 90 formed in a central part of the back cover82. Through holes 41 are formed in the opaque back cover 82 to pass thelifting pins 42 therethrough. The upper surface of the opaque back cover82 is in close contact with the lower surface of the support table 32.Three projections 120 are formed on the lower surface of the back cover82 to form a space 122 between the opaque back cover 82 and the lowersurface covering member 76. Thus the opaque back cover 82 is allowed tomove to prevent the opaque back cover 82 from cracking. Only two of thethree projections 120 are shown in FIG. 2. The projections 120 may beformed on the upper surface of the lower surface covering member 76instead of on the lower surface of the opaque back cover 82.

The opaque back cover 82 is made of, for example, cloudy, opaque quartzglass containing numerous fine bubbles. The opaque back cover 82intercepts and reflects heat radiated from the lower surface of thesupport table 32. The opaque back cover 82 may be made of any opaque,heat-resistant material and it is desirable that the opaque back cover82 has a high reflectance.

The respective surfaces of the covering members made of transparentquartz glass, namely, the peripheral surface covering member 74, thelower surface covering member 76, the support post covering member 78and the lower end covering member 80, are finished by a surfaceroughening process, such as a sandblasting process, and have fineirregularities. The anchoring effect of the fine irregularities makesunnecessary films deposited on those surfaces difficult to peel off.

A thermocouple, not shown, is attached to the support table 32 tomeasure the temperature of the support table for temperature control.The support table 32 is provided with gas supply ports for introducingan inert gas, such as N₂ gas or Ar gas, onto the back surface of thewafer W to transmit heat to the wafer W at a high heat transfer rate.

The operation of the thermal processing system will be described.

A carrying arm, not shown, holds a new semiconductor wafer W, carriesthe semiconductor wafer W through the opened gate valve 18 and theopening 16 into the processing vessel 4, and places the semiconductorwafer W on the raised lifting pins 42. Then, the lifting pins 42 arelowered to seat the wafer W on the upper surface of the support table32, more specifically, on the bottom surface of the central recess 84formed in the upper surface of the upper surface covering member 72.

Subsequently, source gases, such as some of TiCl₄, H₂, NH₃, WF₆, SiH₄,PET and O₂, are supplied at controlled flow rates, respectively, intothe shower head 6. The source gases are jetted through the gas jettingholes 10 into the processing space S. The vacuum pump, not shown,connected to the exhaust pipe 36 is operated continuously to suckatmospheres in the processing vessel 4 and the exhaust trapping space22. The opening of the pressure regulating valve is regulated tomaintain the processing space S at a predetermined process pressure. Thewafer W is heated at temperatures between about 400 and about 700° C.Thus, a thin film of Ti, TiN, W, WSi or Ta₂O₅ is deposited on a surfaceof the wafer W.

It is possible that heavy metals slightly contained in the support table32 are introduced into the processing vessel 4 by thermal diffusionduring the film depositing process in which the support table 32 madeof, for example, AlN is heated at high temperatures. According to thepresent invention, the support table 32 is covered entirely with theupper surface covering member 72 made of a heat-resistant materialexpected not to cause metal and organic contamination, such as SiC, andthe peripheral surface covering member 74 and the lower surface coveringmember 76 made of heat-resistant, transparent quartz glass expected notto cause metal and organic contamination. Therefore, the diffusion ofheavy metals into the processing vessel 4 can be prevented and thesemiconductor wafer W can be prevented from being contaminated withheavy metals and organic substances. The contamination, namely, metalcontamination and organic contamination, can be sufficiently effectivelyprevented only by the upper surface covering member 72, the peripheralsurface covering member 74 and the lower surface covering member 76.

The support post 30 made of, for example, AlN is completely covered withthe support post covering member 78 made of, for example, transparentquartz glass. Covering the surface of the holding member 62 fixedlyholding the lower end part of the support post 30 and the surface of thebase plate 56 with the lower end covering member 80 made of transparentquartz glass can further improve the contamination preventing effect.

Heat generated by the resistance heater 38 embedded in the support table32 can be efficiently transferred to the wafer W to heat the wafer Wefficiently because the upper surface covering member 72 interposedbetween the support table 32 and the wafer W is made of a materialhaving a thermal conductivity higher than that of transparent quartzglass, such as SiC. The upper surface covering member 72 may be made ofquartz glass. Experiments proved that the temperature difference betweenthe resistance heater 38 and the wafer W decreases when the uppersurface covering member 72 is made of quartz glass instead of SiC.

As the film deposition process proceeds to deposit desired film on thesurface of the wafer W, unnecessary films are deposited inevitably onthe exposed surfaces of the covering members 74, 76, 78 and 80. Sincethe surfaces of the covering members 74, 76, 78 and 80 are finished by asurface roughening process and fine irregularities are formed in thosesurfaces, the anchoring effect of those surfaces provided with the fineirregularities makes the unnecessary films deposited on those surfacesdifficult to peel off. Therefore, the period of the maintenance work,such as a cleaning process, can be extended and the operating ratio ofthe thermal processing system can be increased accordingly.

Unnecessary films tend to deposit in patches on the lower surface of thelower surface covering member 76 covering the lower surface of thesupport table 32 during the film deposition process. In the conventionalthermal processing system, the unnecessary films deposited in patchesdevelop an uneven heat radiation distribution on the support table. Inthe thermal processing system of the present invention, unnecessaryfilms deposited in patches do not develop an uneven heat radiationdistribution because the annular, opaque back cover 82 covers the lowersurface of the support table 32 entirely. Therefore, the support table32 is heated so as to radiate heat in a uniform heat radiationdistribution and is heated in a desired uniform temperaturedistribution, namely, uniform intrasurface temperature distribution evenif unnecessary films are deposited in patches on the lower surface ofthe lower surface covering member 76 and, consequently, the wafer W canbe heated in a uniform intrasurface temperature distribution.

When the resistance heater 38 is divided into sections to heat zones ofthe support table 32 individually, the frequency of temperature tuningduring the film deposition process can be reduced. Since the opaque backcover 82 is capable of reflecting heat radiated by the support table 32to suppress the loss of radiation heat, the thermal efficiency of theresistance heater 38 can be increased accordingly.

Although the thermal processing system in this embodiment is providedwith those covering members, only the opaque back cover 82 may be usedto cover the lower surface of the support table 32. Even if only lowersurface of the support table 32 is covered with the back cover 82, thesupport table 32 and the wafer W can be heated in a highly uniformintrasurface temperature distribution even if unnecessary films depositin patches, the loss of radiation heat can be suppressed, and hence thethermal efficiency of the resistance heater 38 can be increasedaccordingly.

The two covering members, namely, the lower surface covering member 76and the opaque back cover 82, are disposed on the lower side of thesupport table 32 in the thermal processing system. The lower surfacecovering member 76 may be omitted and the opaque back cover 82 may bewelded to the upper end of the support post covering member 78.

The thermal processing system has high maintainability because only thecovering members 72, 74, 76, 78 and 80 need to be cleaned by a wet ordry cleaning process.

In the thermal processing system embodying the present invention, boththe support table 32 and the support post 30 supporting the supporttable 32 are made of AlN, the support table 32 and the support post 30may be made of any suitable materials other than AlN without departingfrom the scope of the present invention.

A support table structure 229 in a second embodiment according to thepresent invention will be described with reference to FIGS. 4 to 9.Referring to FIG. 4, the support table structure 229 includes a supporttable 232 and a support post 230. The support table 232 and the supportpost 230 are made of a highly heat-resistant, highly corrosion-resistantmaterial, such as transparent quartz glass. The support table 232 andthe support post 230 are covered with an upper surface covering member272, a peripheral surface covering member 274, a lower surface coveringmember 276, a support post covering member 278, a lower end coveringmember 280 and an opaque back cover 282. As shown in FIG. 6, the supporttable 232 is a three-layer structure formed by superposing a top plate300A, a middle plate 300B and a bottom plate 300C in that order andwelding together the top plate 300A, the middle plate 300B and thebottom plate 300C. The thin upper surface covering member 272 made of anopaque material, such as SiC is removably attached to the top plate300A. A wiring groove 302 is formed in the upper surface of the middleplate 300B so as to extend over the entire upper surface of the middleplate 300B. A carbon heating element of a resistance heater 238 is laidin the wiring groove 302. The resistance heater 238 is divided aplurality of concentric circular sections. The wiring groove 302 may beformed in the lower surface of the top plate 300A. The resistance heater238 may be a two-layer heater having two vertically superposed heatinglayers. The support table 232 may be provided with additional quartzplates if the number of heating layers requires.

Wiring holes 303 are formed in proper parts of the middle plate 300B andthe bottom plate 300C. Power supply lines connected to the resistanceheater 238 are passed through the wiring holes 303. A wiring groove 305for holding the power supply lines is formed in the lower surface of themiddle plate 300B so as to extend radially toward the center of thesupport table 232. The wiring groove 305 may be formed in the uppersurface of the bottom plate 300C. The top plate 300A, the middle plate300B and the bottom plate 300C are joined together by welding to buildthe support table 232 after installing the heating element of theresistance heater 238 and the power supply lines 240 in and along thewiring grooves 302 and 305. The upper end of the cylindrical supportpost 230 made of, for example transparent quartz glass is welded to acentral part of the lower surface of the support table 232.

The power supply lines 240 are gathered in a central part of the supporttable 232 and are extended downward from the substantially central partof the support table 232. The vertically extending part of the powersupply lines 240 are covered with, for example, quartz tubes 239. Theupper ends of the quartz tubes 239 are welded to the lower surface ofthe bottom plate 300C. A thermocouple holding hole 304 is formed throughthe bottom plate 300C and the middle plate 300B so as to reach the lowersurface of the top plate 300A. A thermocouple 306 for measuringtemperature for temperature control is inserted in the thermocoupleholding hole 304.

A purge gas supply hole 308 is formed through the top plate 300A, themiddle plate 300B and the bottom plate 300C to introduce a purge gasonto the back surface of the wafer W. A vertical gas supply pipe 310(FIG. 6) made of transparent quartz glass is connected to the purge gassupply hole 308. The outlet of the purge gas supply hole 308 opens in asubstantially central part of the support table 232 so as to distributea purge gas uniformly over the upper surface of the support table 232.An opaque shielding member 312 is disposed adjacent to a lower end partof the support post 230 to shield sealing members 260 and 266 (FIG. 4),such as O rings, from heat radiated by the support table 232. Morespecifically, a cylindrical first opaque member 312A made of, forexample, opaque quartz glass and forming a middle part of the supportpost 230 is welded to the support post 230. The length of the firstopaque member 312A is, for example, on the order of 70 mm.

A second opaque member 312B having the shape of a disk and made of, forexample, opaque quartz glass is fitted in the first opaque member 312A.An annular third opaque member 312C made of, for example, opaque quartzglass is disposed so as to cover the sealing members 260 and 266, andthe support post covering member 278 is set on the third opaque member312C. The opaque members 312A, 312B and 312C intercept radiant heatradiated by the support table 232 toward the sealing embers 260 and 266to protect the sealing members 260 and 266 from the thermal damage. Theterm, “opaque quartz glass” signifies quartz glass capable ofintercepting heat rays and radiant heat, such as cloudy quartz glasscontaining numerous fine bubbles or colored quartz glass. The entiresupport post 230 or a lower part, extending down from the first opaquemember 312A, of the support post 230 may be made of opaque quartz glass.A groove is formed in the holding member 262 and the third opaque member312C, and a gas supply pipe defining a gas supply passage 314 is held inthe groove. The gas supply pipe 310 is installed outside the supportpost 230, and the upper and the lower end of the gas supply pipe 210 arewelded to the support table 232 and a flange 252 formed on the lower endof the support post 230, respectively. Thus the gas supply pipe 210 isheld firmly in place. Since the gas supply pipe 310 is installed outsidethe support post 230, the plurality of power supply lines 240 can beheld inside the support post 230. A gas supply passage 314 is formedthrough a bottom member 228 and a base plate 256 so as to communicatewith the gas supply pipe 310.

A cover assembly will be described. Referring to FIG. 8, the coverassembly is formed by assembling the upper surface covering member 272having the shape of a disk and capable of covering a wafer support part,for supporting a semiconductor wafer W thereon, of the upper surface ofthe support table 232, the peripheral surface covering member 274 havingthe shape of a ring and capable of covering a peripheral part of thesupport table 232 and of partly or entirely covering the side surface ofthe support table 232, the lower surface covering member 276 capable ofpartly or entirely covering the side surface of the support table 232and of covering the lower surface of the support table 232, the supportpost covering member 278 capable of entirely covering the side surfaceof the support post 230, and the lower end covering member 280 forcovering a lower end part of the support post 230. The peripheralsurface covering member 274 is seated on a peripheral part of the uppersurface covering member 272. The opaque back cover 282 having an annularshape is held in contact with the lower surface (back surface) of thesupport table 232 between the lower surface of the support table 232 andthe lower surface covering member 276. The lower surface covering member276 covers the lower surface of the opaque back cover 282.

Those covering members 272, 274, 276, 278 and 280 and the back cover 282are made of heat-resistant, corrosion-resistant materials. Since a waferW is seated directly on the upper surface covering member 272, the uppersurface covering member 272 is made of a ceramic material scarcelycausing contamination, such as metal contamination, and having a highthermal conductivity, such as SiC. The opaque back cover 282 is made ofa material scarcely causing contamination, such as metal contamination,and scarcely transmitting heat, such as opaque quartz glass. The othercovering members 274, 276, 278 and 280 are made of a material scarcelycausing metal contamination, such as transparent quartz glass.

The upper surface covering member 272 made of SiC having a high thermalconductivity has the shape of a thin, circular plate. The upper surfacecovering member 272 is provided with a central recess 284 for receivingand supporting a wafer W directly therein. The depth of the centralrecess 284 is approximately equal to the thickness of the wafer W. Aperipheral part 285 of the upper surface covering member 272 isdepressed to form a step. The upper surface covering member 272 isremovably placed on the support table 232 so as to cover the uppersurface of the support table 232 substantially entirely. The uppersurface covering member 272 is provided with through holes 241 throughwhich lifting pins 242 (FIG. 1) extend upward. The thickness of theupper surface covering member 272 is, for example, on the order of 6.5mm.

The peripheral surface covering member 274 made of transparent quartzglass has the shape of a ring having an inverted L-shaped cross sectionand is capable of partly or entirely covering the side surface of thesupport table 232. The peripheral surface covering member 274 isremovably put on the support table 232 and covers a peripheral part ofthe upper surface of the support table 232. The upper wall of theperipheral surface covering member 274 is seated on the depressedperipheral part 285 of the upper surface covering member 272. Theperipheral surface covering member 274 can be removed from the uppersurface covering member 272. The thickness of the peripheral surfacecovering member 274 is, for example, about 3 mm.

The lower surface covering member 276 made of transparent quartz glassand the support post covering member 278 made of transparent quartzglass are joined together by welding. The lower surface covering member276 is a circular vessel capable of partly or entirely covering the sidesurface of the support table 232 and of entirely covering the lowersurface of the support table 232. The lower surface covering member 276is provided in its central part with an opening 288 for receiving anupper end part of the support post 230 as shown in FIG. 4. The upper endof the support post covering member 278 is welded to the edge of theopening 288. The lower surface covering member 276 is capable ofremovably receiving the entire support table 232 therein. The insidediameter of the side wall of the peripheral surface covering member 274is slightly greater than the outside diameter of the side wall of thelower surface covering member 276. As shown in FIG. 4, the peripheralsurface covering member 274 and the lower surface covering member 276are separably combined together by closely fitting the side wall of thelower surface covering member 276 in the side wall of the peripheralsurface covering member 274 so that a lower end part of the side wall ofthe peripheral surface covering member 274 and an upper end part of theside wall of the peripheral surface covering member 274 overlap eachother

Thus, the side surface of the support table 232 is completely covered.Through holes 41 are formed in the bottom wall of the lower surfacecovering member 276. The lifting pins 42 (FIG. 1) are extended throughthe through holes 41. The support post covering member 278 welded to thelower surface covering member 276 has an inside diameter slightlygreater than the outside diameter of the flange 252 of the support post230. The support post covering member 278 is seated on the holdingmember 262 as shown in FIG. 4. When the support table 232 needs to beremoved, the support table can be extracted upward from the integrallyformed assembly of the lower surface covering member 276 and the supportpost covering member 278. The respective wall thicknesses of the lowersurface covering member 276 and the support post covering member 278are, for example, between about 3 and about 5 mm.

The opaque back cover 282 is formed in an annular shape to cover theentire lower surface (back surface) of the support table 232 excluding apart joined to the support post 230. The support post 230 is passedthrough a central opening 290 formed in a central part of the back cover282. Through holes 41 are formed in the opaque back cover 282 to passthe lifting pins 42 therethrough. The opaque back cover 282 is disposedbetween the lower surface of the support table 232 and the lower surfacecovering member 276. The opaque back cover 282 is supported by threeprojections, not shown, on the lower surface covering member 276. Theopaque back cover 282 is made of, for example, cloudy, opaque quartzglass containing numerous fine bubbles. The opaque back cover 282intercepts heat radiated from the lower surface of the support table232.

As shown in FIG. 4, the flange 252 is formed on the lower end of thecylindrical support post 230 made of, for example, transparent quartzglass. In FIG. 4, the interior structural members of the support table232 and the lifting pins 42 are omitted. The bottom wall 228 is providedwith a central opening 254 of a predetermined size. A base plate 256made of, for example, an aluminum alloy and having a diameter slightlygreater than that of the opening 254 is placed on the upper surface ofthe bottom wall 228 and is fastened to the bottom wall 228 with bolts258. The sealing member 260, such as an O ring, is held between theupper surface of the bottom wall 228 and the lower surface of the baseplate 256 to seal hermetically the gap between the bottom wall 228 andthe base plate 256.

The support post 230 is stood on the base plate 256. A holding member262 is made of, for example, an aluminum alloy and has the shape of aring having an inverted L-shaped cross section. The holding member 262is put on the flange 252 so as to cover the flange 252 and is fastenedto the base plate 256 with bolts 264 to hold the flange 252 fixedlybetween the holding member 262 and the base plate 256. A cushioningmember 263 is held between the upper surface of the flange 252 and thejoining surface of the holding member 262 to prevent the breakage of theflange 252. The cushioning member 263 is an annular carbon sheet of athickness on the order of 0.5 mm that has a cushioning effect and doesnot produce particles. A sealing member 266, such as an O ring, is heldbetween the upper surface of the base plate 256 and the lower surface ofthe flange 252 to seal hermetically the gap between the base plate 256and the flange 252. The base plate 256 is provided with a big throughholes 268. The power supply conductors 240 are extended outside throughthe through hole 268. The interior of the cylindrical support post 230is at the atmospheric pressure. The support post 230 may be airtightlysealed.

The lower end covering member 280 made of transparent quartz glasscovers the exposed surfaces of the holding member 262 and the base plate256. The lower end covering member is a ring having an inverted L-shapedcross section. The thickness of the lower end covering member 280 is,for example, between about 2.75 and about 7.85 mm.

The diameter of the flange 252 is slightly smaller than the insidediameter of the support post covering member 278. Thus the support post230 can be extracted upward from the support post covering member 278after removing the base plate 256 and the holding member 262 byunfastening the bolts 258 and 264.

The surfaces of the cover assembly of transparent quartz glass, namely,the peripheral surface covering member 274, the lower surface coveringmember 276, the support post covering member 278 and the lower endcovering member 280 are finished by a surface roughening process, suchas a sandblasting process, and have fine irregularities. The anchoringeffect of the fine irregularities makes unnecessary films deposited onthose surfaces difficult to peel off.

The operation of the thermal processing system will be described.

A carrying arm, not shown, holds a new semiconductor wafer W, carriesthe semiconductor wafer W through the opened gate valve 18 and theopening 16 into the processing vessel 4, and places the semiconductorwafer W on the raised lifting pins 42. Then, the lifting pins 42 arelowered to seat the wafer W on the upper surface of the support table232, more specifically, on the bottom surface of the central recess 284formed in the upper surface of the upper surface covering member 272.

Subsequently, source gases are supplied at controlled flow rates,respectively, into the shower head 6. The sources gases are such asTiCl₄, H₂ and NH₃ when a Ti film is to be deposited. The source gasesare TiCl₄ and NH₃ when a TiN film is to be deposited. The source gasesare jetted through the gas jetting holes 10 into the processing space S.The vacuum pump, not shown, connected to the exhaust pipe 36 is operatedcontinuously to suck atmospheres in the processing vessel 4 and theexhaust trapping space 22. The opening of the pressure regulating valveis regulated to maintain the processing space S at a predeterminedprocess pressure. The wafer W is heated at temperatures between about400 and about 600° C. Thus, a thin film of Ti or TiN is deposited on asurface of the wafer W.

It is possible that heavy metals slightly contained in the support table232 are introduced into the processing vessel 4 by thermal diffusionduring the film depositing process in which the support table 232 madeof, for example, AlN is heated at high temperatures. According to thepresent invention, the support table 232 and the support post 238 aremade of a heat-resistant, corrosion-resistant transparent quartz glassscarcely containing heavy metals and such. Therefore, heat can beefficiently transferred to the wafer W contamination, such as metalcontamination can be prevented. Since the support table 232 iscompletely covered with the upper surface covering member 272 made of amaterial that will not cause contamination, such as metal contamination,such as SiC, the peripheral surface covering member 274 made oftransparent quartz glass that is highly heat-resistant and will notcause contamination, such as metal contamination, and the lower surfacecovering member 276 made of transparent quartz glass, the diffusion ofheavy metals into the processing vessel 4 can be prevented and thesemiconductor wafer W can be prevented from being contaminated withheavy metals. The contamination, namely, metal contamination, can besufficiently effectively prevented only by the upper surface coveringmember 272, the peripheral surface covering member 274 and the lowersurface covering member 276.

Completely covering the support post 230 made of quartz glass with thesupport post covering member 278 made of, for example, transparentquartz glass enables the further improvement of the effect on preventingcontamination, such as metal contamination. Covering the surface of theholding member 262 fixedly holding the lower end part of the supportpost 230 and the surface of the base plate 256 with the lower endcovering member 280 made of transparent quartz glass can further improvethe effect on preventing contamination, such as metal contamination.

Heat generated by the resistance heater 238 embedded in the supporttable 232 can be efficiently transferred to the wafer W to heat thewafer W efficiently because the upper surface covering member 272interposed between the support table 232 and the wafer W is made of amaterial having a thermal conductivity higher than that of transparentquartz glass, such as SiC. Since the thermal conductivity of transparentquartz glass is higher than that of opaque quartz glass, heat can betransferred more efficiently when the support table 232 is made oftransparent quartz glass than when the support table 232 is made ofopaque quartz glass.

Since the upper surface of the support table 232 is covered with theopaque upper surface covering member 272 made of, for example, SiC, atemperature distribution on the resistance heater 238 is not directlyreflected on the wafer W. Consequently, the uniformity of temperaturedistribution on the surface of the wafer W can be improved. Thus theupper surface covering member 272 has the function of a temperatureequalizing plate.

As the film deposition process proceeds to deposit a desired film on thesurface of the wafer W, unnecessary films are deposited inevitably onthe exposed surfaces of the covering members 272, 274, 276, 278 and 280.Since the surfaces of the covering members 272, 274, 276, 278 and 280are finished by a surface roughening process and fine irregularities areformed in those surfaces, the anchoring effect of those surfacesprovided with the fine irregularities makes the unnecessary filmsdeposited on those surfaces difficult to peel off. Therefore, the periodof the maintenance work, such as a cleaning process, can be extended andthe operating ratio of the thermal processing system can be increasedaccordingly.

Unnecessary films tend to deposit in patches on the lower surface of thelower surface covering member 276 covering the lower surface of thesupport table 232 during the film deposition process. In theconventional thermal processing system, the unnecessary films depositedin patches develop an uneven heat radiation distribution on the supporttable. In the thermal processing system of the present invention,unnecessary films deposited in patches do not develop an uneven heatradiation distribution because the annular, opaque back cover 282 isdisposed under the support table 232 at a distance between about 1 andabout 2 mm from the lower surface of the support table 232 so as tocover the lower surface of the support table 232 entirely. Therefore,the support table 232 can be heated so as to radiate heat in a uniformheat radiation distribution and is heated in a desired uniformtemperature distribution, namely, uniform intrasurface temperaturedistribution, even if unnecessary films are deposited in patches on thelower surface of the lower surface covering member 276 and,consequently, the wafer W can be heated in a uniform intrasurfacetemperature distribution.

When the resistance heater 238 is divided into sections to heat zones ofthe support table 232 individually, the frequency of temperature tuningduring the film deposition process can be reduced. Since quartz glasshas a small coefficient of thermal expansion, the support table 232 willnot break even if the zones of the support table 232 are heated atgreatly different temperatures, respectively, and hence the zones of thesupport table 232 can be heated at desired temperatures, respectively.Since the opaque back cover 282 is capable of suppressing the loss ofradiation heat, the thermal efficiency of the resistance heater 238 canbe increased accordingly.

Although the lower surface covering member 276 and the opaque back cover282 are placed under the lower surface of the support table 232 in thisembodiment, the lower surface covering member 276 may be omitted and theopaque back cover 282 may be directly welded to the upper end of thesupport post covering member 278.

The thermal processing system has high maintainability because only thecovering members 72, 74, 76, 78 and 80 need to be cleaned by a wet ordry cleaning process.

Since the support table 232 in this embodiment is made of transparentquartz glass having a coefficient of thermal expansion smaller than thatof a ceramic material, such as AlN, used for making the conventionalsupport table, the support table 232 has an improved heat resistance andcan be heated at a high temperature higher than an upper limittemperature at which the conventional support table can be heated. Sincethe support table 232 is made of quartz having a small coefficient ofthermal expansion, the support table 232 will not break even ifmagnitudes of power supplied to the zones are greatly different.Experiments showed that whereas a conventional support table made of AlNbroke at about 700° C., the support table 232 of the present inventionmade of transparent quartz glass did not break when heated at about 720°C. In some cases, power of different magnitudes is used for heating aninner zone and an outer zone of the support table 232 to heat thesupport table 232 in an optimum temperature distribution. Experimentsshowed that the support table 232 did not break when input power ratio,namely, the ratio of the magnitude of input power for heating the innerzone to that of input power for heating the outer zone, was changed inthe range of about 0.2 to about 1, and the support table 232 was heatedat temperatures between 400 and 720° C. Additionally, the support table232 did not break when the temperature of the support table 232 wasraised up to 1200° C.

FIG. 9 is a graph showing data obtained by the experiments on thedependence of intrasurface temperature distribution on the support table232 on process pressure for temperatures in the range of 400 to 720° C.The process pressure was varied in the range of 10⁻¹ to 666 Pa. Asobvious from FIG. 9, the uniformity of intrasurface temperaturedistribution is within ±0.7% and the mean uniformity of intrasurfacetemperature distribution is within ±0.5% for temperatures in the rangeof 400 to 720° C. In the conventional support table, the uniformity ofintrasurface temperature distribution is on the order of ±1.2%. Theexperiments showed that the uniformity of intrasurface temperaturedistribution in the support table 232 is equal to or better than that inthe conventional support table.

Since the resistance heater 238 is embedded in the support table 23built by laminating the quartz glass plates, the power supply lines 240emerge downward from the central part of the support table 232. Thesupport table 232 constructed by superposing and welding together thetop plate 300A, the middle plate 300B and the bottom plate 300C, whichare made of quartz glass, can be completely separated from theprocessing vessel 4. Deposition of films on the upper surface of thesupport table 232, the lower surface of the upper surface coveringmember 272 and the side surface of the thermocouple holding hole 304 canbe prevented by jetting out a purging gas from the upper surface of thesupport table 232.

A support table structure in a modification of the support tablestructure in the second embodiment may be provided with a temperatureequalizing plate 401 made of an opaque material, such as SiC, disposedbetween an upper surface covering member 372 and a top plate 300A asshown in FIG. 10. The temperature equalizing plate 401 contributes touniformly heating the wafer W.

As shown in FIG. 10, gas passage 414 communicating with a gas supplypipe 410 may be formed outside a flange 252 and through an opaque thirdmember 312C, a holding member 262, a base plate 256 and a bottom wall228.

Projections 420 may be formed on the lower surface of an opaque backcover 282 to form a space 422 between the lower surface of the opaqueback cover 282 and a lower surface covering member 276.

As shown in FIGS. 11 and 12, in a support table structure in anothermodification of the support table structure in the second embodiment,the diameter of an upper surface covering member 572 may besubstantially equal to that of a support table 532 to cover the uppersurface of the support table 523 entirely with the upper surfacecovering member 572. The support table structure may be provided with atemperature equalizing plate corresponding to the temperature equalizingplate 401 mentioned in connection with FIG. 10.

The upper surface covering member 572 excluding a peripheral partthereof is raised slightly to form a raised part 524. A recess 584 isformed in the raised part 572. A wafer W is received in the recess 584.The inside surface of an annular ridge 526 is tapered downward to form aconical surface 526A. When a wafer W is put on the upper surfacecovering member 572, the conical surface 526A guides the wafer W tocenter the wafer W on the upper surface covering member 572. Aperipheral surface covering member 574 is put on the upper surfacecovering member 572 such that the upper wall thereof is seated on aperipheral part of the upper surface covering member 572.

As shown in FIGS. 11 and 12, as a modification of the support tablestructure in the first and second embodiment, the side surface of thesupport table 532 is covered with an opaque quartz cover 528. Thermalefficiency can be improved by reflecting heat radiating from the supporttable 532 by the opaque quartz cover 528. The opaque quartz cover 528shown in FIG. 11 is formed integrally with an opaque back cover 582covering the lower surface of the support table 532 and an opaque sidecover covering the side surface of the support table 532. The opaqueside cover and the opaque back cover 582 may be separate members. Theopaque quartz cover 528 covering the side surface of the support table532 can be applied to the support table structures shown in FIGS. 2 and4 for the same effect.

When the support table 532 is made of AlN, the upper surface coveringmember 572 is made of AlN or transparent or opaque quartz glass. Whenthe support table 532 is made of transparent quartz glass as mentionedin connection with FIG. 10, the upper surface covering member 572 ismade of AlN or opaque quartz glass.

In the foregoing embodiments, the support table 232 and the support post230 are covered with the covering members. A support table structure 629in a third embodiment according to the present invention shown in FIG.13 is not provided with any covering members. As shown in FIG. 13, thesupport table structure 629 does not have any members corresponding tothe peripheral surface covering member 274, the lower surface coveringmember 276, the support post covering member 278 and the lower endcovering member 280 shown in FIG. 4. An opaque back cover 282 isdisposed in contact with the lower surface of a support table 232. Evenif unnecessary films are deposited in patches on the lower surface ofthe opaque back cover 282, the opaque back cover 282 protects thesupport table 232 from the detrimental thermal effect based on theunnecessary films. An upper surface covering member 272 is placed on theupper surface of the support table 232 to improve the uniformity ofintrasurface temperature distribution on a wafer.

In the support table structure 629 shown in FIG. 13, the exposedsurfaces of the support table 232 and the support post 230 made oftransparent quartz glass may be finished by a surface rougheningprocess, such as a sandblasting process, as measures for preventingcontamination with particles.

In the embodiments shown in FIGS. 4 and 13, the support table 232 andthe support post 230 may be made of opaque quartz glass instead oftransparent quartz glass. Only the bottom plate 300C may be made ofopaque quartz glass and the opaque back cover 282 covering the lowersurface of the support table 232 may be omitted.

Although the foregoing embodiments have been described on an assumptionthat the support table structure is used for a thermal CVD process, thepresent invention is applicable also to plasma CVD systems, etchingsystems, oxidizing and diffusing systems and sputtering systems.

Although the invention has been described as applied to processing asemiconductor wafer, it goes without saying that the present inventionis applicable to processing LCD substrates, glass substrates and thelike.

The term “transparent quartz glass” signifies quarts glass not perfectlytransparent having a transmittance higher than a predetermined thresholdtransmittance as well as completely transparent quartz glass. The term“opaque quartz glass” signifies quartz glass having a transmittancelower than a predetermined threshold transmittance as well as completelyopaque quartz glass. The predetermined threshold transmittance isdetermined on the basis of whether or not the thermal energy of lighttransmitted by an object has effect on the support table or theprocessing vessel.

1. A support table structure comprising: a support table, for supportinga workpiece thereon to subject the workpiece to a predetermined thermalprocess in a processing vessel, provided with a heating means forheating the workpiece; and a support post standing on the bottom of theprocessing vessel and supporting the support table, characterized by aheat-resistant upper surface covering member, a heat-resistant sidesurface covering member and a heat-resistant lower surface coveringmember respectively covering an upper, a side and a lower surface of thesupport table, and a heat-resistant, opaque back cover disposed underthe lower surface of the support table, an upper surface of a peripheralpart of the upper surface covering member is contiguously covered with apart of the side surface covering member, the peripheral part of theupper surface covering member being connected with the side surfacecovering member so as to enclose the heating means, the lower surfacecovering member covers the lower surface of the opaque back cover, andthe covering members excluding the upper surface covering member and theopaque back cover are made of transparent quartz glass, and the surfacesof the covering members made of transparent quartz glass are finished bya surface roughening process to prevent films deposited thereon frompeeling off.
 2. The support table structure according to claim 1,wherein the upper surface covering member has a diameter substantiallyequal to that of the support table, a raised part is formed on the uppersurface of the upper surface covering member, and a recess for receivingthe workpiece is formed in the raised part.
 3. The support tablestructure according claim 1, wherein the side surface of the supporttable is covered with an opaque covering member made of opaque quartzglass.
 4. The support table structure according to claim 1, wherein aspace is formed between the opaque back cover and the lower surfacecovering member.
 5. The support table structure according to claim 4,wherein projections project from the lower surface of the opaque backcover to define the space between the opaque back cover and the lowersurface covering member.
 6. The support table structure according to anyone of claims 1, 4, and 5 wherein the opaque back cover is made ofopaque quartz glass.
 7. The support table structure according to claim1, wherein the upper, the side and the lower surface covering member andthe support post covered with a heat-resistant support post coveringmember constitute a cover assembly, the lower surface covering memberand the support post covering member are formed integrally in a singlemember, and the cover assembly can be assembled and disassembled.
 8. Asupport table structure comprising: a support table for supporting aworkpiece thereon to subject the workpiece to a predetermined thermalprocess in a processing vessel; and a support post standing on thebottom of the processing vessel and supporting the support table;characterized in that the support table and the support post are made ofquartz glass, a heating means is embedded in the support table, thesupport post has as a cylindrical shape, and power supply lines forsupplying power to the heating means are extended outside the supporttable through a central part of the support table and are extended downthrough the cylindrical support post, and the support table is built bybonding together a top plate, a middle plate and a bottom plate, wiringgrooves for holding the heating means are formed in either the lowersurface of the top plate or the upper surface of the middle plate, and awiring groove for holding the power supply lines connected to theheating means is formed in either the lower surface of the middle plateor the upper surface of the bottom plate.
 9. The support table structureaccording to claim 8, wherein the upper surface of the support table iscovered with an opaque temperature-equalizing plate.
 10. The supporttable structure according to claim 8, wherein the support table isprovided with a purging gas supply pore to supply a purging gas over theupper surface of the support table, and a gas supply quartz pipe isconnected to the purging gas supply pore.
 11. The support tablestructure according to claim 10, wherein the gas supply quartz pipe isextended outside the support post and has upper and lower ends welded tothe support table and the support post, respectively.
 12. The supporttable structure according to claim 8, wherein the quartz glass istransparent.
 13. The support table structure according to claim 8,wherein a heat-resistant, opaque back cover is disposed under the lowersurface of the support table.
 14. The support table structure accordingto claim 8, wherein the upper, the side and the lower surface of thesupport table are covered with upper, side and lower surface coveringmembers, respectively.
 15. The thermal processing system according toclaim 14, wherein the heating means for heating the support table isdivided into inner and outer heating sections respectively correspondingto inner and outer zones in the support table.
 16. The support tablestructure according claim 8, wherein the support post is stood up on acushioning member to prevent the breakage of the support post.
 17. Thesupport table structure according to any one of claims 1 and 8, whereinthe side surface of the support post is covered with a heat-resistantsupport post covering member.
 18. The support table structure accordingto any one of claims 1 and 8, wherein a sealing member is disposed neara lower joining part of the support post, and the sealing member isshielded from heat radiated by the support table by an opaque shieldingmember.
 19. The support table structure according to claim 18, whereinthe support post is made of an opaque material, the support post isinternally provided with an opaque member to protect the sealing memberdisposed near the lower joining part of the support post from heatradiated by the support table.
 20. A thermal processing systemcomprising: a processing vessel capable of being evacuated; the supporttable structure according to any one of claims 1 and 8; and a gas supplysystem for supplying process gases into the processing vessel.